2002 blazer 2dr 4x4. Won’t stay running and missing. Starts up and the idle fluctuates between 300-800 rpm till it stalls. If I stomp the gas at low idle I can hear a spark knock for just a quick sec then it seems to smooth out at 3-4K. Also it acts like it has no power when in gear probly from the missing out? I pulled 3 codes. P0341 , P0335 , and P0101. Would any of these cause the others to throw a code? I’ve changed plugs, wires, cap, rotor with AC Delco. I’ve tested fuel pressure and it hits 60-61 at prime and sets at 55-58psi for over 15mins. Trying to figure out my next move before dumping in to much money.

 

Could the timing chain have slipped?

 

Also I noticed if u hold it at a steady 2k rpm or so u can hear a miss every couple secs. Almost like a hiccup?

 

Any gas in the oil? I ask as that could be an indicator of a leaky (flooding) fuel injection spider.

 

The codes come up as camshaft position sensor, crankshaft position sensor and mass air flow sensor. Should I just buy all three or should I start with certain one first?

 

No gas in oil.

 

Rereading your original post and this last one, here is what comes into my mind:

I would first try to find a reason for why all three sensors are giving errors simultaneously.

If it were just one error being reported, then perhaps the associated sensor could be at fault. The odds for all three sensors to go bad simultaneously is pretty slim. Besides, these errors arose simultaneously with the engine running poorly which could mean that the sensors are correct. Depending on the sensor, an engine could run even though the sensor is bad.

From what you reported, simultaneous errors with the crank position, cam position and air flow would be consistent with the timing chain having slipped a tooth as it is the timing chain that ensures that the camshaft that opens and closes the valves which controls the airflow is timed correctly with the position of the pistons. If they are off, the wrong amount of air gets in at the wrong time along with the spark happening at the wrong time since the distributor is driven by the camshaft. The result is an engine getting fuel and spark at the wrong time and barely running. How your engine is running is reminiscent of how the 318 in an old Dodge Dart ran when its timing chain slipped by a little bit. At higher speeds it might run a bit better but still with little power.

The official GM shop manuals might help with further diagnosis. But a professional shop could do that for you. Once you have their diagnosis in hand, you can decide if you want to do the repair yourself.

The thing about a timing chain slipping is that it can happen in an instant and cause the connected systems to all go out of whack simultaneously. Depending on the engine, a slip of a little bit won't cause any permanent damage and is fixed by installing a new chain and gears set and realigning the gears.

In principle it is a straight forward repair that involves taking off the water pump and the timing chain cover. However with so much crammed into the engine compartments on our Blazers, it probably is a bit of a hassle to get to it.

Look for videos of Blazers, or other cars with 4.3l engines, that have slipped their timing chain and see if the symptoms match yours.

Perhaps someone else here will chime in for a second opinion? Anyone, Anyone? Bueller??

For your sake, I hope my diagnosis is wrong and I'll be interested to hear what others think could be wrong.

Good Luck!

P.S. What is the mileage on the engine?
P.P.S. BTW, To your question if one going bad could effect the engine operation and thus the signals reported by the other two? For that I'll admit ignorance. With the interconnected nature of the systems on these engines I guess it could be possible but I would not know how to diagnose that.

 

I noticed when I start it when cold it seems to run good for about a min. I wonder if the coil pack breaking down is a possibility?

 

Also when driving down the highway it seems to be fine while holding a steady speed

 

I've noticed on the forum descriptions of how to test the coil. You might look for those posts and test that.

The only time I had a coil go out on me it was on my 68 Mustang. The symptoms were that it would run fine but under hard acceleration the motor would die, as if there was no more spark, and when I slowed down it would run again.

The coil had partially shorted out so that the voltage at the output was not quite as much as it should have been.